Method for treating wastes by solidification

ABSTRACT

A method for treating aqueous liquid and semi-liquid wastes by solidification comprising the steps of mixing with the waste a dry water-reactive solidification agent comprising cement, a dry water absorbent material, and a powdered alkali metal silicate in a quantity sufficient to convert the mixture into a chemically and physically stable solid end product substantially insoluble in water and which contains no substantially free-standing water, and allowing the mixture to set to a sedentary mass. Additive agents such as surfactants, fixatives, waterproofing agents, coloring agents, and the like are also disclosed as assisting in the solidification reaction by reacting with certain constituents in the waste.

This application is a continuation of application Ser. No. 510,152,filed June 30, 1983 now abandoned which is a continuation of Ser. No.339,621, filed Jan. 15, 1982 now abandoned.

BACKGROUND

1. Field of the Invention

This invention relates in general to waste treatment, and specificallyrelates to a method for treatment of aqueous liquid and semi-liquidwaste sludges and slurries by solidification and/or fixation.

2. Description of the Prior Art

The processing of hazardous or offensive waste materials produced bymunicipalities and industries has reached critical importance inmodern-day society. Concern for the quality of life and the environmenthave compelled governmental agencies to promulgate legislation to insurethat future generations will not suffer from the effluvia of ourpresent-day society. Under the regulations which implement thesegovernmental edicts, waste must be discarded in a fashion which isnon-offensive and presents little or no threat to the air, water, andland upon which the waste is ultimately disposed. The U.S. Congress in1976 enacted Subtitle C of the Resource Conservation and Recovery Act of1976 (RCRA), Public Law 94-580, for the purpose of instituting anational hazardous waste control program similar in function to thepreviously promulgated Air Pollution and Water Pollution Controlprogram.

The U.S. Environmental Protection Agency, charged with theresponsibility for implementing and supervising the hazardous wastecontrol program called for under RCRA, promulgated in 1980 a series ofregulations which require that certain sludges, slurries and otherliquid wastes containing specified hazardous materials may no longer bedeposited in landfills without pre-treatment, stabilization, anddewatering. Wastes must additionally have acceptable toxicity levels asmeasured by certain established tests before they can be discarded in alandfill. One primary objective of these governmental requirements is toachieve a non-flowing consistency of the waste by reduction of theliquid content or increase of the solid content to eliminate thepresence of free liquids prior to final disposal in the landfill. Theend result of this and other similar legislation and regulations is thatmany liquid or semi-liquid wastes containing hazardous materials willrequire dewatering, chemical fixation, solidification, or somecombination thereof, prior to ultimate disposal.

Chemical fixation and solidification processes have found recent favorfor detoxifying hazardous materials and for producing solid wasteshaving physical properties suitable for ultimate disposal in landfills,ocean dumping, etc. For example, U.S. Pat. No. 3,837,872, discloses amethod for treating liquid wastes by adding an aqueous solution of analkali metal silicate and a silicate setting agent, which converts thewaste into a chemically and physically stabe solid product. The patentto Thompson, U.S. Pat. No. 3,980,558, discloses a method for treatingliquid wastes by adding a solidification agent consisting essentially ofhydraulic cement.

The terminology of chemical fixation and solidification has not beenconsistent in the prior art and there has been an aura of mystiquesurrounding such waste treatment processes, due primarily to the factthat until recently most of the waste treatment systems offered wereconsidered proprietary. Such terms as "encapsulation", "crystalcapture", and "pseudo mineral" often appear in the prior art instead ofdiscussions concerning the operation of such systems, most likelybecause the actual chemical reactions involved are complex and notcompletely understood.

There is also a tendency in the prior art to confuse the terms "chemicalfixation", "stabilization" and "solidification". "Stabilization" isessentially a pretreatment process which alters wastes to preventfurther chemical reactions, e.g. the use of lime in biological sludgesto kill or inactivate micro-organisms so that the sludge will notundergo further biological decomposition. "Chemical fixation" refers tothe chemical technology used to destroy, de-toxify, immobilize,insolublize, or otherwise render a waste component less hazardous orless capable of finding its way into the environment. The term oftendenotes a chemical reaction between one or more waste components in asolid matrix, either introduced deliberately or preexisting in thewaste. For example, the ion exchange of heavy metals within the aluminosilicate matrix of a cementitious solidification agent is a chemicalfixation. There is a wide variety of chemical fixation techniques knownin the art for preparing waste residues for solidification,encapulation, or disposal without solidification.

The term "solidification" is the transformation of a waste residue intoa solid physical form which is more suitable for storage, burial,transportation, ocean disposal, or re-use in processes such as highwaypaving. Solidification does not, by itself, affect the hazard potentialof the waste. Solidification may reduce the hazard potential by means ofcreating a barrier between the waste particles and the environment,limiting permeability of the waste to water, or reducing the affectedsurface area of the waste available for diffusion. There are varioustypes of solidification known in the art which do not incorporatechemical fixation. Moreover, the solidification of waste does not alwaysinvolve a chemical process, e.g., drying, dewatering and filtration arephysical processes which are sometimes considered "solidification".

Conventional chemical fixation and solidification techniques sometimesdo not adequately treat wastes to obtain suitable end products fordisposal. Generally, these prior art fixation and solidificationtechniques are unsuitable for sludges and slurries containing a lowsolids percent, for example, less than 10% to 20% by weight. Dewateringprocesses frequently cannot achieve a true solid and are sometimessubject to reversion to the original state by the simple addition ofwater. Pure absorption processes such as the addition of clays or limesuffer also from the problem of reversion to the original state.Moreover, in some wastes, the absorbed liquid phase of the waste can besqueezed out of the "solidified" material under mechanical pressure suchas may occur in a landfill or even during handling or transportingprocesses.

The nuclear industry in the 1950's recognized the need for preventingthe reversion of wastes into a liquid phase. Early methods in thisindustry employed simple absorption techniques such as the addition ofvermiculite, or solidification by making a concrete mixture with verylarge quantities of Portland cement. Large quantities were required toassure that there would be no free standing water after curing of thecement. This inevitably resulted in a relatively large ratio of cementto waste and a large volume of end waste product which must betransported and disposed of. Substantial volume increases can makedisposal prohibitively expensive in landfills which predicate disposalprices on volume.

Moreover, the Nuclear Regulatory Commission has stated in a preliminarydraft of 10 CFR Part 61 that any nuclear wastes containing liquids mustbe immobilized by solidification to an end product in a dry,free-standing, homogeneous, monolithic matrix which is not readilydispersible, friable or soluble and which contains not more than 0.5% orone gallon per container, whichever is less, of noncorrosive liquids.Under these standards, liquids that have been immobilized by only theaddition of absorbent materials such as diatomaceous earth orvermiculite are not acceptable waste forms.

The cement-silicate solidification process such as disclosed in U.S.Pat. No. 3,837,872 referenced above is designed to provide asolidification waste treatment method which does not allow reversion tothe liquid phase after gel and which has a reduced volume of endproduct. The method is usable with a wide variety of wastes includingthose emanating from manufacturing, metal producing operation, and thelike, which contain large concentrations of toxic polyvalent metals.This cement-silicate technology was developed primarily for use withwater-based, primarily inorganic wastes with low to moderate solidscontent (1-30%). The technology was specifically designed for use withcontinuous processing equipment wherein a liquid silicate solution canbe added in a controlled manner so as to control the set or "gel" time.The gel time is controlled by the concentrations of cement and liquidsilicate as well as the composition of the waste. In many applications,liquid silicate solidification systems have such short gel times thatsetting begins before the mixed waste leaves the processing equipment.

A problem with conventional cement-liquid silicate solutionsolidification treatment processes is that the two components of thesystem must be added to the waste separately since pre-mixing of suchwaste treatment materials would result in immediate setting thereof. Therapid setting rate of a cement and liquid silicate solidificationsystem, together with the fact that the components must be addedseparately, makes the system usable only with continuous processes andvery difficult to use in batch waste treatment.

The use of a dry soluble silicate instead of a liquid silicate solutiontogether with cement for waste treatment has provided a differentproblem. This type of waste treatment requires more time for the gelreaction to occur since the silicate must solublize before it can gel.During this time, some settling of the sludge may occur inbatch-processing treatment facilities or in continuous processes withlow flow rates or inadequate agitation. If there is settling of thesludge prior to gel, free-standing water will occur on the top of thewaste, which renders the treatment incomplete and unsatisfactory.

BRIEF SUMMARY OF THE INVENTION

Briefly described, the present invention is a method for treatingaqueous liquid and semi-liquid wastes to render them fit for ultimatedisposal comprising the steps of adding to the waste a drywater-reactive solidification agent comprising cement, a dry waterabsorbent material, and a powdered alkali metal silicate in a quantitysufficient to convert the mixture into a consolidated chemically andphysically stable solid which is substantially insoluble in water andwhich contains substantially no free standing water. Thereafter, themixture is allowed to set to a sedentary mass. A preferredsolidification agent for use in the method of the present invention hasa ratio of cement to water absorbent material ranging from between about1:19 to about 47.5:1, a ratio of cement to alkali metal silicate rangingfrom between about 2:1 to about 200:1, and a ratio of alkali metalsilicate to water absorbent ranging from between about 1:3,800 to about3:1.

After the introduction of the solidification agent and the allowance ofsufficient time for the mixture to set, the resultant end product is asolid material varying in consistency from a rock-like solid to afriable material, depending upon the particular waste treated, theamount of solidification agent added, and the relative proportion ofcement, water absorbent material, and alkali metal silicate.

The solid structure of the end product is a pseudo-mineral formed of asilicate matrix which is based on tetrahedrally coordinated siliconatoms alternating with oxygen atoms along the backbone of a linearchain. There is strong ionic bonding between adjacent chains to formpolymer matrices which are very similar to many of the natural pyroxeneminerals. Consequently, the end product displays properties of highstability, high melting point, and substantially imperviousness toleaching of waste constituents encapsulated in the matrix.

The solidification agent is characterized by a relative low cost andwidespread availability of the chemical ingredients, which are generallynon-toxic in themselves. The method is therefore relatively easy topractice since the chemical processes normally occur at ambienttemperatures and pressures and without unique or special processingequipment. Advantageously, only relatively low volume increases areresultant, in contrast to conventional solidification agents whichconsist mainly of cement. The end product is further inert toultraviolet radiation and shows extremely high resistance tobiodegradation. Because of the matrix structure, the end productdisplays low water solubility and permeability, and mechanical andstructural characteristics suitable for disposal in landfills, oceandisposal, and construction of highway roadbeds and the like.

Accordingly, it is an object of the present invention to provide animproved method for waste treatment.

It is a further object of the present invention to provide an improvedsolidification agent useful in applications requiring waste treatment bysolidification.

It is a further object of the present invention to provide a method fortreating liquid and semi-liquid waste which produces a substantiallysolid end waste material having suitable physical and chemicalcharacteristics for use in a landfill or other areas requiringrelatively inert filler material.

It is a further object of the present invention to provide a method fortreating aqueous liquid and semi-liquid waste which does not undesirablyincrease the volume of the end waste product to the point where landfilldisposal is economically infeasible.

It is a further object of the present invention to provide a method fortreating aqueous liquid and semi-liquid wastes which produces an endwaste product having acceptable toxicity levels as measured by currentlyprevailing governmental regulations concerning same.

It is a further object of the present invention to provide a method fortreating aqueous liquid and semi-liquid wastes whose final end wasteproduct is a solid material possessing chemical properties substantiallyimpervious to leaching and which substantially encapsulates non-solublehazardous materials.

It is a further object of the present invention to provide a method fortreatment of aqueous liquid and semi-liquid wastes which ischaracterized by the use of a relatively low cost solidification agent,the constituents of which are widely available and generally non-toxic.

It is a further object of the present invention to provide a method fortreating aqueous liquid and semi-liquid wastes which is characterized bythe use of a solidification agent which may be pre-mixed in desiredproportions, which is relatively easy to use by simple addition of theagent to the waste, and which involves chemical processes which normallyoperate at ambient temperatures and pressures without unique or specialprocessing equipment.

It is a further object of the present invention to provide an end wasteproduct of waste treatment which is characterized by a relatively lowvolume increases, inertness to ultraviolet radiation, high resistance tobiodegradation, low water solubility and permeability, and possessesmechanical and structural characteristics suitable for disposal in alandfill.

These and other objects, features, and advantages of the method of thepresent invention will become apparent after a review of the followingdetailed description of the disclosed embodiments and the appendedclaims.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT

The method of the present invention comprises the steps of adding to anaqueous liquid or semi-liquid wastes a dry water-reactive solidificationagent comprising cement, a dry water absorbent material, and a powderedalkali metal silicate in a quantity sufficient to convert the mixtureinto a consolidated chemically and physical stable solid productsubstantially insoluble in water and which contains substantially nofree-standing water. The waste is then thoroughly mixed with thesolidification agent and allowed to set for a period of time sufficientto render the mixture a sedentary mass.

The end product of the method of the present invention is a solidstructure formed of a basic silicate matrix which is based ontetrahedrally coordinated silicon atoms alternating with oxygen atomsalong the backbone of a linear chain. The charged side groups of thechain, in this case oxygen, when reacted with polyvalent metal ions,result in strong ionic bonding between adjacent chains to formcross-linked three-dimensional polymer matrices which are very much likemany of the natural pyroxene minerals. Thus, the end product itself isactually a pseudo-mineral. This type of structure displays highstability, a high melting point, and, depending upon the specificformulation, produces a product varying from a rigid, friable structuresimilar to many soils to a hard, monolithic, synthetic rock-likematerial.

In addition to the basic components of the solidification agent, variousminor component additives may also be used to adapt the basicsolidification agent to a particular waste. Also, additives whichinsolublize and precipitate specific waste components, especially thetoxic metals, may also be included in the formulation of thesolidification agent. For example, additives comprising fixatives,waterproofing agents, surfactants, and the like satisfy certain desiredpurposes, which are discussed in detail below.

The resultant solidified end product displays other properties whichmake the treated waste suitable for various final disposal uses. Forexample, the lowered permeability and susceptibility to leaching rendersthe solidified waste suitable for use in a landfill. The end productformed from the chemical reaction is thermodynamically and kineticallystable under normally encountered ambient temperatures and pressures.Consequently, such environmental factors as ground water activity, windand rain erosion, biological degradation, and ultraviolet radiation onlyminimally affect the solidified waste product. If the solidified wasteis to be buried or covered as is normally the case, then the effects oferosion and ultraviolet radiation do not apply. The use of the inorganicsiliceous portion of the solidification agent provides a strongimperviousness to the affects of ambient ground water and biologicaldegradation. The basic chemistry of these systems is the same as that ofcommon rocks, clay, concrete, glass and the like which are known to beamong the most stable physical forms. Consequently, the waste productformed by practice of the present invention can be expected to changevery slowly in the ground as a function of time, on the same scale asthat of natural rocks and minerals. Moreover, the stable matrix issubstantially impervious to leaching of the waste constituents from thematrix under leaching tests currently required by governmental agencies.

The solidification agent disclosed herein for use in the method of thepresent invention comprises cement, a dry powdered alkali metal silicateand a dry water absorbent material. The formulation range of theseprimary components varies from between about 10-90% by weight forcement, from between about 0.1-20% by weight of powdered alkali metalsilicate, and from between about 3-50% by weight of water absorbentmaterial. Minor additives such as hydrated lime, iron oxide,surfactants, waterproofing agents, and fixatives may be added inquantities sufficient to treat particular waste constituents.

The alkali metal silicates preferred for use in the solidification agentare soluble sodium silicates. However, other soluble alkali metalsilicates such as potassium silicates, lithium silicates, and the likeare suitable if available. These soluble silicates may also be formedfrom metasilicates, orthosilicates, and the like from sodium, potassium,lithium, and the like. Thus, it will be appreciated that silicate"polymers" or polysilicates are therefore included as suitable alkalimetal silicates useful in the present invention.

The primary requirement for a soluble silicate for use in the presentinvention is that it dissolve rapidly in water at ambient temperaturesand pressures. Suitable soluble sodium silicates (SiO₂ :Na₂ O) areusually manufactured by fusing soda ash (sodium carbonate) and silicasand to form a glass, then crushing the glass to a fine powder. Thisresults in an anhydrous product having relatively low ratios of SiO₂:Na₂ O, such as less than 2:1. Ratios of SiO₂ :Na₂ O as high as 3.22:1are virtually insoluble in water at normal temperatures and pressuresand must be formed by dissolving the chemicals in high pressure steam tomake sodium silicate solutions which are spray dried to yield ahydrated, water soluble powder.

Commercial soluble silicates suitable for use in the present inventioninclude grade Uniflo 26 sodium metasilicate, pentahydrate, manufacturedby Diamond Shamrock Corporation of Cleveland, Ohio, having a ratio ofSiO₂ :Na₂ O of 0.995:1 and a percentage of water of 42%; special gradeS-25 anhydrous sodium metasilicate also manufactured by Diamond ShamrockCorporation having a SiO₂ :Na₂ O ratio of 1.03:1 and a percentage ofwater less than 1%; and grade G hydrous sodium silicate manufactured byPhiladelphia Quartz Company of Valley Forge, Pa., having a ratio of SiO₂:Na₂ O of 3.22:1 and a percentage of water of about 19%.

The cement used in the present invention is preferably a Portland cementsince it has been found that such cements give the best results. Any ofthe various grades categorized as Portland cement can successfully beused, but generally, type I is preferable because it is the most widelyavailable and lowest cost cement. Other grades may be used either forcost or availability reasons in specific situations or where othergrades may perform better with a specific waste by actual testing.

The cement-alkali metal silicate solidification system has been found tobe readily adaptable to a large variety of water-based wastes. However,the solidification system has also been found to be sensitive to certainwaste constituents which act as inhibitors or otherwise interfere withsolidification. The interactions between the waste constituent and thechemicals are extremely complex because many different reactions occursimultaneously, especially with wastes containing a variety of reactivepollutants. Three general classes of interactions which have beenidentified include reactions between the sodium silicate and the wastebeing treated, reactions between the silicate and certain reactivecomponents such as the calcium ion of the Portland cement, and thereaction of Portland cement itself with water such as hydrolysis andhydration. These reactions and the ability of the resultant end productto encapsulate and hold waste constituents are discussed more fully inU.S. Pat. No. 3,837,872, the disclosure of which is incorporated hereinby reference.

Certain chemical waste constituents which have been identified assolidification inhibitors fall within two basic categories: inhibitorsof the cement-setting reaction, and inhibitors or precipitators of thesilicate or of the cement-silicate mix. Some known cement settinginhibitors include borates; phosphates; sulfide ions; sodium arsenate;sulfates in high concentrations; oil in high concentrations; certainmetal salts including lead, zinc and copper; organics in variousconcentrations; and very finely divided particulate matter. Inhibitorsor precipitators of the silicate or of the cement-silicate mix includeammonia or ammonium compounds, active anaerobic conditions, highconcentrations of aromatic organics, pH conditions less than 4,nitrates, high concentrations of metal ions, and water soluble organics.

When any of the known inhibitors or precipitators are present in thewaste being treated, the gel time of the cement-silicate mix is moredifficult to predict and control. Often, free-standing water will befound on the top of the solidified waste when precipitation has occurredor when settling of certain waste constituents in the sludge occursprior to gelling or setting. This free-standing water is a significantproblem in conventional alkali metal silicate-cement solidificationsystems since the water can contain toxic substances in solution.

Water excretion can also occur with conventional alkali metalsilicate-cement solidification with overmixing or hard freezing whichcan break the initial, relatively delicate gel. Phase separation canalso result in free-standing water where an immiscible hydrophobicliquid component separates from an emulsion of water and oil.

The addition of a dry water absorbent material to the alkali metalsilicate-cement mixtures solves many of the problems associated withmany conventional waste treatment system. Certain water absorbentmaterials have been found to act as a viscosity control agent, reactant,surface agent, settling control agent, permeability reducer,ion-exchanger, constituent absorbent, reaction controller, andanti-inhibition agent. Although some of these functions might seemcontradictory, for any given waste only a few of these characteristicsare evident. The combination of water absorption and viscosity controlprevents settling of the waste and solids contained therein until thegelation reaction can occur. The balance between settling and gelationis critical with cement-soluble silicate treatment systems. If gelationoccurs too slowly and settling occurs too rapidly, water excretion willoccur on top of the solid. If gelation occurs too rapidly, operationalproblems with handling the waste emerge. Therefore, the addition of awater absorbent material provides the surprising result that thereaction time can be controlled as well as excess water can be absorbedand held until the reaction has occurred.

To be useful in the present invention, a water absorbent material musthave fine particles and high surface area, so that hydrophilicproperties are evident. Various types of clays have been found to be themost suitable water absorbent material. Certain clays seem to act asactivators, which aid and control the set of the gel. The clays preventthe excretion of surface water in the treatment of fast settling wastes.The settling rate of the solids in the waste is to be controlledprimarily by the addition of more or less clay.

Since clays are natural minerals which occur in many locations, thecharacteristics are extremely varied. Particular types of clays whichhave been found suitable for use in present invention include typeKaolinite, grade Barden manufactured by I.M. Huber Company of Huber,Ga., having a fineness of 325 mesh (94%); type Bentonite (sodium), gradeHigh-Gel, manufactured by American Colloid Company of Skokie, Ill.,having a fineness of 200 mesh (65%); type Montmorillonite (calcium),grade Ren-Fre GBW, manufactured by Oil Dri Corporation of Chicago, Ill.,having a fineness of 200 mesh (80%); and type Attapulgite, grade Attagel40, manufactured by Engelhard Minerals & Chemicals Corporation ofEdison, N.J., having a fineness of 0.14 microns.

It will be appreciated by those skilled in the art that other clays,other similar mineral products, and other water absorbent materials maybe successfully employed in the present invention. For example, non-claypoducts, such as natural gums, natural and synthetic gelling agents, andthe like may also be successfully used since the primary purpose iswater absorption and viscosity control. Specific types of non-clay waterabsorbent materials useful in the present invention include diatomaceousearth, type Celaton MN41, manufactured by Eagle Picher Corporation,Cincinnati, Ohio; calcium silicate, type Micro-Cel, manufactured byJohns-Mansville Corporation, Littleton, Colo.; fumed silica, typeCab-O-Sil, manufactured by Cabot Corporation, Tuscola, Ill.; acrylicpolymer, type Permasorb 29, manufactured by National Starch & ChemicalCorp., Bridgewater, N.J.; styrene polymer, type Imbiber Beads,manufactured by Dow Chemical Company, Midland, Mich.; natural gum, typeGuar Gum, manufactured by Meer Corporation, North Bergen, N.J.;organo-aluminum compounds, type aluminum isopropylate, manufactured byChattem Chemicals, Chattanooga, Tenn.; and cellulosics, type Cellosize,manufactured by Union Carbide Corporation, Danbury, Conn. Generally,however, mineral products such as clays provide the best combination ofeconomics, availability, stability and function.

A typical formulation of the solidification agent disclosed herein asproportions of cement to water absorbent material ranging from betweenabout 1:19 to about 47.5:1, cement to alkali metal silicate ranging frombetween about 2:1 to about 200:1, and alkali metal silicate to waterabsorbent ranging from between about 1:3,800 to about 3:1. The relativeproportions of the components are varied to adjust to the desiredfriability or solidity of the end product, the rate of gel, the presenceof inhibiting agents, and the proportion of solid waste product to waterin the waste sludge or slurry. A typical formulation for a high solidswaste sludge might be 1.5 pounds per gallon of a mixture of 65% Portlandcement, 10% sodium silicate, and 20% clay, with a coloring agent (ironoxide) of about 1%, a surfactant of about 0.1% and lime (for acidneutralization) about 3.9%. Typical additive rates may vary from about10% by weight to about 50% by weight, or from about 1 to about 5 poundsper gallon of waste.

The overall operative ranges of ingredients for a preferred formulationof the solidification agent including additives may be expected to be,by percent of weight of the formulation, Portland cement, 5-95%;powdered soluble alkali metal silicate; 0.1-30%; clay, 2-80%; lime (foralkalinity adjustment), 0-40%; iron oxide or other colorant, 0-3%;surfactant, 0-0.1%; and other additives, 0-1.0%. The setting time mayrange from about 5 minutes to one or more days, depending upon theformulation, addition rate, waste composition, and ambient temperatureand humidity. Typically, an initial setting time of 30 to 60 minutes isdesirable for most applications. After initial setting, hardeningcontinues for several days, with 75% of the hardness typically achievedwithin 10 to 20 days. The basic formulation of Portland cement, sodiumsilicate, and clay is generally considered non-hazardous and is easy tohandle and use. Since the formulations tend to be alkaline, and sincenearly all formulations can contain very fine powders which can beirritating to mucous membranes, it is generally advisable to utilizecaution in handling the chemicals, for example, eye protection and dustmasks should be used.

In determining the proper formulation, the question of volume increaseassociated with the end product must be considered. This factor can beextremely important when the end product is to be disposed in landfillsor transported. In the future, volume increase may be the most importantsingle factor in formulating a solidification agent if, as is suspected,the value of landfill disposal space for chemical wastes continues torise at a rapid rate. Volume increase may be controlled as a function ofthe formulation, additive ratios, and properties of the waste beingtreated. Anticipated volume increases of the end waste product fortypical formulations of the solidification should range from betweenabout 4% to about 25%.

In formulating a solidification agent for use in the present invention,the particular waste being treated should be analyzed. Usually, themedium in which the waste is dispersed is a water-based waste which maycontain emulsions of liquid organic substances such as oil. The primaryphysical properties of the waste which affect the formulation includethe solids content, the particle size distribution and shape, viscosityand specific gravity. It is generally desirable to have a high solidscontent because smaller amounts of solidification agent may be added,provided that the solidification agent does not itself react withsolids. The chemical nature of the waste also affects the solidificationprocess. In addition to cement setting inhibitors which are discussedabove, acceleration of the chemical reaction and biological activity canaffect the properties of the end waste product. Accelerators forPortland cement setting and curing include calcium chloride and sodiumsilicate. Biological activity also causes problems and is generallyunpredictable on a theoretical basis. A biologically active organicsludge often produces hydrogen sulfide and other sulfur compounds whichcan affect the setting reaction. It has been found that sometimes thewaste will not harden in the presence of the sulfur compounds.

In order to counteract the effect of inhibitors, accelerators, or otherwaste constituents which affect the basic cement-silicate solidificationprocess or the fixation of waste constituents in the solidified matrix,it may sometimes be desirable to include additives in the formulation ofthe solidification agent. Fixatives, waterproofing agents, andsurfactants are additives which can assist the solidification of wastescontaining certain types of solidification-affecting constituents. Clay,lime, and surfactants all act to eliminate the effects of inhibitors.Clay and lime, and to some extent cement, fix metals by absorption,ion-exchange and hydroxide formation, and gradually react with insolublesilicates to form the basis for the cement. The settling rate of solidsin the waste may be controlled primarily by the addition of more clay,and to a lesser degree by the addition of lime.

A fixative, which is a compound which reacts with one or moreconstituents of the waste to form a less soluble compound, therebyretarding or preventing leaching of the waste, may be added to theformulation. For example, a waste containing lead carbonate is solublein acid and therefore requires a fixative to insolublize the leadcompound. The insoluble form of the specific constituent is thenentrapped in the inorganic polymeric matrix and completely immobilized.Fixatives useful in the present invention include gypsum, plaster ofparis (calcium sulfate hemihydrate), and diammonium phosphate.

A waterproofing agent is a compound which does not react chemically withthe waste but prevents or retards leaching by sealing the waste particlewithin the solidified waste mass. Calcium stearate is a waterproofingagent useful in the present invention.

A surfactant is a compound which may be added to allow reaction to occurbetween a particular waste constituent and another constituent.Generally, surfactants enhance or accelerate the solidificationreaction. Surfactants useful in the present invention includedetergents, wetting agents, defoamers and the like. Although themechanism by which surfactants operate is not clearly understood, it isthought that surfactants decrease interfacial tension between particlesand thereby allow reaction between the waste particle and anotherconstituent. Certain surfactants counteract the inhibiting effect of anaerobic condition in a biologically active waste sludge, and therebyallow the basic solidification agent to operate without requiring thatuneconomical levels of the agent be added.

Surfactants perform a variety of functions including emulsification, gelstabilization, the wetting of hydrophobic waste constituents, anddeactivation of certain inhibitors. Triton X-100, a sulfonatedalkylphenol having a hydrophile-lipophile balance number of 13.5,manufactured by Rohm & Haas Company, Philadelphia, Pa. is a surfactantwhich may be used to counteract the inhibiting effect of anaerobicconditions in a biologically active waste sludge. The choice ofsurfactant depends upon the function required and the prevalentelectrical surface charge on the suspended particulate or colloidalmatter. The surfactants may usually be added in low amounts, usuallyonly from between about 0.001 to about 1% of the total additive volume.

A mixing indicator or colorant such as iron oxide or the like may alsobe added. These substances, originally used as a colorant to indicatewhen mixing is complete, have been found to function in an unknownmanner as activators in the setting reaction of the solidification agentdisclosed herein. Other metal oxides may be used for the same purpose,but iron oxide is particularly suited for the method of the presentinvention due to its low cost, high coloring power and non-toxicity.

Commercial iron oxide grades found operative in the present inventioninclude grade Mapico Red 347, manufactured by Cities Service Company,Atlanta, Ga., and grade RO 3097, manufactured by Pfizer ChemicalCompany, Atlanta, Ga. Finer particle sizes are preferable for a coloringagent, since particle size affects coloring power and effectiveness asan activator.

Lime, either anhydrous (quick) or hydrated, may be added to neutralizeexcess acidity in the waste. To a certain extent lime will act as awater absorbent, so the amount of clay may have to be adjustedaccordingly. Many of the commercially available limes, including groundlimestone (agricultural lime) are suitable for acid neutralization.

The following examples are set forth to illustrate the method of thepresent invention and are not intended to be limitative thereof. In theexamples, the compressive strength of the waste is defined as unconfinedcompressive strength measured in tons per square foot, as measured by aconventional penetration strength tester such as the Model CL700 POCKETPENETROMETER manufactured by Soiltest, Inc., of Evanston, Ill. Chemicalcosts are reported in cents per gallon of as-received waste prior totreatment and are based upon the approximate cost of bulk procurement ofsuch materials by commercial entities in December, 1981.

EXAMPLE 1

A waste sludge from the chemical conversion coating of aluminum in theaircraft industry, comprising emulsified cutting oils, organic compoundsand trace amounts of metals, having solids by weight of 3%, pH of 7.5and low viscosity, was treated in accordance with the method of thepresent invention as described hereinabove. The formulation achievedcompressive strength of 4.2 tons/sq.ft. after curing for 10 days. Theresults of this treatment are indicated below:

    ______________________________________                                                                      Cost                                            Solidification Agent                                                                           Vol. Increase (%)                                                                          ¢/gal.                                     ______________________________________                                        3.6 lb/gal. Portland                                                                           25           31.5                                            cement + 0.4 lb/gal.                                                          Sodium metasilicate                                                           Grade S-25 + 0.95                                                             lb/gal. Barden                                                                grade kaolin + 0.05                                                           lb/gal. iron oxide                                                            grade RO 3097.                                                                ______________________________________                                    

EXAMPLE 2

A digested sewage sludge from the activated sludge process at amunicipal sewage plant, comprising phosphates, nitrogen compounds,organics, and the metals chromium, lead, copper and zinc, having solidsby weight of 2%, pH of 5.8 and low viscosity, was treated in accordancewith the method of the present invention as described hereinabove. Theformulation achieved compressive strength of 3.2 tons/sq.ft. aftercuring for 10 days. The results of this treatment are indicated below:

    ______________________________________                                                                       Cost                                           Solidification Agent                                                                            Vol. Increase (%)                                                                          ¢/gal.                                    ______________________________________                                        2.88 lb/gal. Portland                                                                           20           25.2                                           cement + 0.32 lb/gal.                                                         sodium metasilicate                                                           Grade S-25 + 0.76 lb/gal.                                                     Barden grade kaolin +                                                         0.04 lb/gal. iron oxide                                                       grade RO 3097.                                                                ______________________________________                                    

EXAMPLE 3

A rapid settling waste filter cake slurry from the production of organicsurfactants, comprising diatomaceous earth, naphthalene and naphthalenesulfonates, having solids by weight of 65%, pH of 8.8, and moderateviscosity when stirred, was treated in accordance with the method of thepresent invention as described hereinabove. The formulation achievedcompressive strength of 4.5 tons/sq.ft. after curing for 11 days. Theresults of this treatment are indicated below:

    ______________________________________                                                                       Cost                                           Solidification Agent                                                                            Vol. Increase (%)                                                                          ¢/gal.                                    ______________________________________                                        0.96 lb/gal. Portland                                                                           6.5          7.3                                            cement + 0.11 lb/gal.                                                         sodium silicate grade                                                         G hydrous + 0.25 lb/gal.                                                      Barden grade kaolin +                                                         0.01 lb/gal. iron oxide                                                       grade Mapico Red 347.                                                         ______________________________________                                    

EXAMPLE 4

A waste slurry from the pretreatment for painting of metal surfaces,comprising zinc phosphate and small amounts of organics, having solidsby weight of 2%, pH of 3.6, and low viscosity, was treated in accordancewith the method of the present invention as described hereinabove. Theformulation achieved compressive strength of 2.8 tons/sq.ft. aftercuring for 10 days. The results of this treatment are indicated below:

    ______________________________________                                                                        Cost                                          Solidification Agent                                                                            Vol. Increase (%)                                                                           ¢/gal.                                   ______________________________________                                        1.44 lb/gal. Portland                                                                           15            14.2                                          cement + 0.16 lb/gal.                                                         sodium metasilicate                                                           Grade S-25 + 0.68 lb/gal.                                                     Barden grade kaolin +                                                         1.0 lb/gal. hydrated lime +                                                   0.02 lb/gal. iron oxide                                                       grade RO 3097.                                                                ______________________________________                                    

EXAMPLE 5

A lagoon sludge from an oil refinery, comprising oil, silt, metalcompounds, and various organic compounds, having solids by weight of25%, pH of 3.5, and moderate viscosity, is treated in accordance withthe method of the present invention as described hereinabove. Theformulation should achieve compressive strength of at least 2.5tons/sq.ft. after curing for 10 days. The anticipated results of thistreatment are indicated below:

    ______________________________________                                                                       Cost                                           Solidification Agent                                                                            Vol. Increase (%)                                                                          ¢/gal.                                    ______________________________________                                        1.3 lb/gal. Portland                                                                            13           12.5                                           cement + 0.23 lb/gal.                                                         sodium metasilicate                                                           grade Uniflo 26 + 0.65                                                        lb/gal. Ren-Fre GBW                                                           Grade Montmorillonite +                                                       0.25 lb/gal. hydrated                                                         lime + 0.003 lb/gal.                                                          non-ionic surfactant.                                                         ______________________________________                                    

EXAMPLE 6

A waste slurry from an inorganic chemicals manufacturing plant,comprising barium and other metals, silt, and organics, having solids byweight of 5%, pH of 7.5 and low viscosity, is treated in accordance withthe method of the present invention as described hereinabove. Theformulation should achieve compressive strength of at least 3.0tons/sq.ft. after curing for 10 days. The anticipated results of thistreatment are indicated below:

    ______________________________________                                                                       Cost                                           Solidification Agent                                                                            Vol. Increase (%)                                                                          ¢/gal.                                    ______________________________________                                        1.3 lb/gal. Portland                                                                            10           10.5                                           cement + 0.16 lb/gal.                                                         sodium metasilicate                                                           grade Uniflo 26 + 0.4                                                         lb/gal. Ren-Fre GBW                                                           Grade Montmorillonite +                                                       0.12 lb/gal. calcium                                                          sulfate hemihydrate +                                                         0.02 lb/gal. iron oxide                                                       Grade RO 3097.                                                                ______________________________________                                    

EXAMPLE 7

An acidic oily sludge from an oil refinery comprising oil and inorganicsolids, water, metals, having total solids by weight of about 30%, a pHof about 5, with a medium viscosity, is treated in accordance with themethod of the present invention as described hereinabove. Theformulation should achieve compresive strength of about 3 tons/sq.ft.after curing for 10 days. The anticipated results of this treatment areindicated below:

    ______________________________________                                                                       Cost                                           Solidification Agent                                                                            Vol. Increase (%)                                                                          ¢/gal.                                    ______________________________________                                        4 lb/gal. Ren-Fre GBW                                                                           25           20                                             Grade Montmorrillonite +                                                      0.9 lb/gal. Portland                                                          cement + 0.1 lb/gal.                                                          sodium metasilicate Grade                                                     S-25 + 0.05 lb/gal. iron                                                      oxide grade RO 3097.                                                          ______________________________________                                    

EXAMPLE 8

A filter cake from a metal finishing plant comprising mainly metaloxides and hydroxides including cadmium having total solids by weight ofabout 20%, a pH of about 7, with a medium viscosity, is treated inaccordance with the method of the present invention as describedhereinabove. The formulation should achieve compressive strength ofabout 4.5 tons/sq.ft. after curing for 10 days. The anticipated resultsof this treatment are indicated below:

    ______________________________________                                                                        Cost                                          Solidification Agent                                                                            Vol. Increase (%)                                                                           ¢/gal.                                   ______________________________________                                        0.95 lb/gal. Portland                                                                           5             6                                             cement + 0.02 lb/gal.                                                         Barden grade kaolin +                                                         0.03 lb/gal. sodium                                                           silicate Grade G hydrous +                                                    0.01 lb/gal. iron                                                             oxide Grade RO 3097.                                                          ______________________________________                                    

EXAMPLE 9

A filter cake from a metal finishing plant comprising mainly metaloxides and hydroxides including cadmium having total solids by weight ofabout 30%, a pH of about 8, with a high viscosity, is treated inaccordance with the method of the present invention as describedhereinabove. The formulation should achieve compressive strength ofabout 4 tons/sq.ft. after curing for 10 days. The anticipated results ofthis treatment are indicated below:

    ______________________________________                                                                        Cost                                          Solidification Agent                                                                            Vol. Increase (%)                                                                           ¢/gal.                                   ______________________________________                                        0.3 lb/gal. sodium                                                                              5             17                                            silicate Grade G hydrous +                                                    0.6 lb/gal. Portland                                                          cement + 0.1 lb/gal.                                                          Barden grade kaolin +                                                         0.01 lb/gal. iron oxide                                                       grade RO 3097.                                                                ______________________________________                                    

EXAMPLE 10

An alkaline (pH=12-13) fluid-like sludge from an oil refinery comprisingoil, dissolved inorganic solids and organic solids, having a highdissolved solids content by weight of about 30%, with a low-to-mediumviscosity, is treated in accordance with the method of the presentinvention as described hereinabove. The formulation should achievecompressive strength of about 3 tons/sq.ft. after curing for 10 days.The anticipated results of this treatment are indicated below:

    ______________________________________                                                                       Cost                                           Solidification Agent                                                                            Vol. Increase (%)                                                                          ¢/gal.                                    ______________________________________                                        3.8 lb/gal. kaolin +                                                                            20           13                                             0.2 lb/gal. Portland                                                          cement + 0.001 lb/gal.                                                        sodium metasilicate                                                           grade Uniflo 26 + 0.04                                                        lb/gal. iron oxide grade                                                      Mapico Red 347.                                                               ______________________________________                                    

EXAMPLE 11

An alkaline (pH=12-13) fluid-like sludge from an oil refinery comprisingoil, dissolved inorganic solids and organic solids, having a highdissolved solids content by weight of about 30%, with a low-to-mediumviscosity, is treated in accordance with the method of the presentinvention as described hereinabove. The formulation should achievecompressive strength of about 3 tons/sq.ft. after curing for 10 days.The anticipated results of this treatment are indicated below:

    ______________________________________                                                                       Cost                                           Solidification Agent                                                                            Vol. Increase (%)                                                                          ¢/gal.                                    ______________________________________                                        1.9 lb/gal. Imibiber                                                                            20           955                                            Beads + 0.2 lb/gal.                                                           Portland cement + 0.001                                                       lb/gal. sodium metasilicate                                                   grade Uniflo 26 + 0.04                                                        lb/gal. iron oxide grade                                                      Mapico Red 347.                                                               ______________________________________                                    

EXAMPLE 12

A digested sewage sludge from the activated sludge process at amunicipal sewage plant, comprising phosphates, nitrogen compounds,organics, and the metal chromium, lead, copper and zinc, having solidsby weight of 2%, pH of 5.8 and low viscosity, is treated in accordancewith the method of the present invention as described hereinabove. Theformulation should achieve compressive strength of about 3.2 tons/sq.ft.after curing for 10 days. The anticipated results of this treatment areindicated below:

    ______________________________________                                                                       Cost                                           Solidification Agent                                                                            Vol. Increase (%)                                                                          ¢/gal.                                    ______________________________________                                        2.88 lb/gal. Portland                                                                           20           70                                             cement + 0.32 lb/gal.                                                         sodium metasilicate Grade                                                     S-25 + 0.2 lb/gal. fumed                                                      silica + 0.04 lb/gal.                                                         iron oxide grade RO 3097.                                                     ______________________________________                                    

EXAMPLE 13

A waste sludge from the chemical conversion coating of aluminum in theaircraft industry, comprising emulsified cutting oils, organic compoundsand trace amounts of metals, having solids by weight of 3%, pH of 7.5and low viscosity, is treated in accordance with the method of thepresent invention as described hereinabove. The formulation shouldachieve compressive strength of 4.2 tons/sq.ft., after curing for 10days. The anticipated results of this treatment are indicated below:

    ______________________________________                                                                       Cost                                           Solidification Agent                                                                            Vol. Increase (%)                                                                          ¢/gal.                                    ______________________________________                                        3.6 lb/gal. Portland                                                                            25           49                                             cement + 0.4 lb/gal.                                                          sodium metasilicate Grade                                                     S-25 + 0.3 lb/gal.                                                            natural gum type Guar                                                         Gum + 0.05 lb/gal. iron                                                       grade RO 3097.                                                                ______________________________________                                    

Obviously, many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andthe scope thereof, and therefore, only such limitations should beimposed as are indicated in the following claims.

I claim:
 1. A method of treating a batch of aqueous liquid andsemi-liquid wastes to render them fit for ultimate disposal in asedentary mass, comprising the steps of:premixing a solidification agentby admixing cement, a dry water absorbent clay having fine particles,said particles having high surface area, and a powdered alkali metalsilicate, wherein said solidification agent has a ratio of cement toclay between about 1:19 and about 47.5:1, a ratio of cement to alkalimetal silicate between about 2:1 and about 2000:1, and a ratio of alkalimetal silicate to clay between about 1:3,800 and about 3:1; treating thebatch of waste by admixing said premixed solidification agent with thewaste in a quantity sufficient to convert the mixture into a chemicallyand physically stable solid product substantially insoluble in water andwhich contains substantially no free-standing water; and allowing theadmixture to set to a sedentary mass.
 2. The method of claim 1, whereinsaid cement comprises Portland cement.
 3. The method of claim 1, whereinsaid alkali metal silicate comprises sodium silicate.
 4. The method ofclaim 1, wherein said alkali metal silicate comprises sodiummetasilicate.
 5. The method of claim 1, wherein the amount of saidsolidification agent added to the waste is between about one pound pergallon of waste and about five pounds per gallon of waste.
 6. The methodof claim 1, wherein said solidification agent further comprises a mixingindicator to indicate when mixing is complete.
 7. The method of claim 6,wherein said mixing indicator comprises iron oxide.
 8. The method ofclaim 1, wherein said solidification agent further comprises asurfactant.
 9. The method of claim 8, wherein said surfactant comprisesa sulfonated alkylphenol.
 10. The method of claim 1, wherein saidsolidification agent further comprises a fixative.
 11. The method ofclaim 10, wherein said fixative is selected from the group consisting ofgypsum, plaster of paris, and diammonium phosphate.
 12. The method ofclaim 1, wherein said solidification agent further comprises awaterproofing agent.
 13. The method of claim 12, wherein saidwaterproofing agent comprises calcium stearate.